1999 Gm 7500 Cat 3126 OBD11 NO COMUNICATION
suggest that you edit your title...
So, what tool are you plugging into it? And where? The DTC under the dash? A jumper harness under da hood? JPRO? Cat ET?
Welcome to the Forums! Glad to have you. Moved this thread over to the truck forum. If you would like to change the thread title let me know - a more descriptive thread name will garner more responses. Best of luck.